A major component in electricity production is gas turbine engines, which burn hydrocarbon fuels and contribute to carbon emissions and global warming. In order to reduce our carbon footprint, it is crucial that we decrease fuel consumption by increasing engine efficiency. Thermal barrier coatings (TBCs) provide a solution. As thermal insulators, they protect gas turbine superalloys from damaging high heat, allowing higher combustion temperatures and greater engine efficiency. TBCs must not only insulate the metallic components from heat, but should not react with a protective thermally grown oxide (TGO) on the superalloy. Systems of interest to this project must be capable of operating at a maximum temperature of 1700°C (~500°C above current materials) and be stable in contact with the TGO at temperatures up to 1350°C. As a first stage in this project, we are testing the thermochemical stability of two TBCs, HfO₂-YO_1.5 and ZrO₂-YbO_1.5-LaO_1.5, with the most common TGO: AlO_1.5 (alumina). We are precipitating the TBC oxide constituent from precursor solutions, then pyrolyzing the precipitate into powders which we are compacting and sintering into pellets. We are then subjecting the sintered TBC pellets to two experiments. First, we are heat treating to test for high temperature phase stability. Then we are cross-sectioning and imaging the synthesized material using scanning electron microscopy. We expect the results to provide insight on the viability of the candidate HfO₂-YO_1.5 TBC for gas turbine applications. Future work will investigate the diffusion couples with alumina, which we will be heating to test for thermochemical compatibility.